1. Field of the Invention
The present invention relates to a video and audio signal editing and transmitting apparatus for editing and transmitting video and audio signals, more particularly relates to a video-on-demand (VOD) system which provides a desired program selected from among stored video programs such as movies or other video and audio signals to a subscriber when it is demanded or a near-video-on-demand (NVOD) apparatus, that is, what may be called a simplified version of a video-on-demand (VOD) system.
2. Description of the Related Art
Among the video and audio signal editing and transmitting apparatuses now being developed, mention may be particularly made of the video-on-demand (VOD) apparatuses and the near-video-on-demand (NVOD) apparatuses.
A video-on-demand (VOD) system is a digital two-way dialog type broadcast system which provides a video program such as movie requested by a user (subscriber) to the user at his or her home or other location immediately upon demand. With a video-on-demand (VOD) system, a subscriber would be able to view the video program he or she requested at the time requested via a television receiver at his or her own home etc. The content provided by such a video-on-demand (VOD) system would not be limited to movie programs. It would be possible to provide any picture and audio signals corresponding to that picture as well. In the following description, however, reference will be mainly made to the broadcast of a movie program as typical example of the content.
A video-on-demand (VOD) system is supposed to allow a large number of subscribers to request the programs they desire at any time, therefore the amount of the data in the video and audio signals transmitted from the broadcasting station to the subscribers would become enormous. As a result, the transmission capacity of the transmission path and the data processing ability at the broadcasting station side would both have to be large. If the number of the subscribers becomes too large and requests are made from too many subscribers at the same time, there is a good chance that disadvantages would occur in terms of the response time. Of course, installation of a large number of apparatuses capable of performing high speed processing would enable all of these requests to be responded to instantaneously, but this would make the overall system extremely expensive.
To overcome these disadvantages anticipated in video-on-demand (VOD) systems, a near-video-on-demand (NVOD) system has been proposed as a more practical version of a video-on-demand (VOD) system. In a near-video-on-demand (NVOD) system, the same program is sent over a number of channels staggered in time. By selecting from among these channels, it is possible to provide the subscriber with his or her desired program after a short wait or to even allow the subscriber to view the program from a later part he or she particularly desires to see.
While a near-video-on-demand (NVOD) system does not have the instantaneous response time of a video-on-demand (VOD) system in the strict sense of the term, a user can for example start viewing the program he or she desired after just waiting for 10 to 15 minutes at the most after he or she makes the request when the program is sent at 10 or 15 minute time intervals. Therefore, there is no disadvantage in terms of practical use. Further, there are the advantages that realization of such a near-video-on-demand (NVOD) system requires a much simpler configuration of hardware than realization of a video-on-demand (VOD) system and that the processing speed does not have to be as fast as with a video-on-demand (VOD) system.
Further, if a subscriber views the content of a certain program up to the middle of the program and then has to stop for some reason or another, as stated above, he or she can resume viewing the program from the middle by just selecting from among the channels over which the program is being broadcast. Therefore, there is the additional advantage that the subscriber need not view a program at a single long sitting and can stop it midway and can resume viewing from a desired portion later, that is, can view it just like viewing a program recorded on a video tape at a home video cassette recorder.
One of the easiest ways to realize a video on-demand (VOD) system or a near-video on-demand (NVOD) system would be to connect a plurality of digital compression and encoding apparatuses at the transmission stage of a conventional broadcasting system, input their outputs to a digital multiplexing device, and broadcast the result through a modulating device and transmitting device.
However, when adopting such a method for a near-video-on-demand (NVOD) apparatus, it suffers from the disadvantage that the same number of transmission portions of the conventional broadcasting system and the same number of digital compression and encoding devices as the number of the multiple channels become necessary, therefore the entire system would become large in size and, at the same time, the price would become high.
Further, in the conventional hardware configuration, the hardware as a whole is designed for providing near-video-on-demand NVOD service. The functions of the system as a whole are not suitably broken down and the components are not separated. Therefore, this configuration is not suited to partial modification or replacement of the hardware.
Note that while the related art was described with reference particularly to a video-on-demand (VOD) system or a near-video-on-demand (NVOD) system, there are similar disadvantages in also other video and audio signal editing and transmitting apparatuses performing similar processing to these systems.